The present invention relates to a color image processing system which is provided with a color-ghost elimination function and advantageously applied to a simple electrophotographic color copying apparatus and the like.
A color image processing apparatus, wherein image information on an original document or the like is optically read out and recorded on a recording paper by means of an output device such as an electrophotographic color copying apparatus, has been already known.
When using an electrophotographic color copying apparatus as an output device, color image information on an original document or the like is usually separated into a plural types of independent color information (including a non-chromatic type), thereby based on such color information, an independent electrostatic latent image is formed, developed and fixed.
Incidentally, such a color image processing apparatus uses a plurality of photoelectrical conversion elements such as CCDs which serve as means for reading image information, in order to acquire a plural types of information for the corresponding number of colors. If the independent color images respectively read by corresponding CCDs are misaligned with each other, specific color information Ls outputted as different color information.
Such misalignment results in the occurrence of color ghost. A color-ghost also occurs if a power of optical lens is misadjusted, a lens has large chromatic aberration, or noise components other than image signal are involved in the CCD output.
The above-mentioned color image processing apparatus is provided with a color-ghost elimination circuit for eliminating a color-ghost occurring by these reasons.
The color-ghost elimination process is performed referring not only to the pixels to be subjected to color-ghost elimination process but to color information of a plural pixels adjacent the former pixels. In other words, the color-ghost elimination process is performed based on a color pattern constituted with a specific number of pixels.
When using a color pattern composed of a specific number of pixels as mentioned above to eliminate color-ghost, and assuming that a number of types of separated, independent color information is N and a number of pixels to be referred to is M, the ghost elimination process for an object pixel (a pixel being subjected to ghost elimination process) by using M sets of pixels requires at least EQU N.sup.M
sets of color patterns to be referred to.
Accordingly, the numbers of color patterns required, when N=2 to 4, and M=3 to 9, will be as listed in FIG. 21.
A color-ghost occurs when N=3 or larger. Accordingly, a color-ghost is eliminated by providing a number of color patterns to be referred to as listed in FIG. 21.
A smaller number of M is advantageous. However, a larger M may correct an image having a larger ghost. Correspondingly, an ideal M is 7 to 9.
However, if setting value of M at larger value such as 9 and setting value of N at round 4 which means that there are 4 kinds of color to be recorded, the color pattern to be prepared becomes too numerous. Since such color patterns are to be stored in ROM, it may be necessary for above setting to prepare the large ROM in memory capacity. Therefore, the large ROM may incur high cost.
And, such method, has a disadvantage, density readily fluctuates in the course of multi-value conversion, since the method effects the correction only to color codes, not to density information for respective colors.